TV idol Jack was suave with a devilish eye for the ladies. He was an alcoholic, suffered from bipolar disease and was, by all accounts, a terrible father, walking out on the family home when David was three.

He told me Jack was “incapable of being a father” — still, David desperately wanted to make him proud.

But the more success David found, the more Jack resented him. He was as addicted to the fame as the alcohol. It was the latter that cut his life short, aged 49, in 1976.

A drunk Jack was alone in his apartment. Falling asleep, his lit cigarette started a blaze that burned all night.

David hadn’t spoken to Jack in nine months, and it took 15 years of therapy for him to come to terms with their complex relationship.

In 2012 he told me: “With the perspective I have now, I would have been able to forgive him.”

Despite his demons, David was an incredible performer. I watched him striding across the stage during an early tour, wearing a white, rhinestone-encrusted jumpsuit. Girls went wild watching their pin-up.

But it was an abnormal, isolated life lived behind security guards. It was clear he wasn’t fully comfortable with the hysteria.

He told me: “It’s hard to describe what it’s like when you have 70,000 screaming ‘I love you’ at you.”

The fevered crowds that followed him could be dangerous. In May 1974 he played London’s White City stadium for the BBC. It was sunny and so many young, excited girls were there. For some reason I had a real sense of impending doom.

As soon as he came on stage there was an awful rush forwards. I watched from backstage as these little girls were plucked from the crush. Dozens were on stretchers.

A few days later, Bernadette Whelan, 14, unconscious since the crush, became the first fatality at a British pop concert. David was devastated. He went into a terrible decline. He felt responsible.

Their son Beau was the apple of his father’s eye. David said: “Being a good father, that’s the thing I’m most proud of. When Beau says, ‘Will you come to my baseball game?’ I go. My dad would say yes and not show up.”